The present invention relates to machining apparatus and process in which a cold-gas-blow cooling is used.
In a grinding, cutting or other machining operation, a grinding or cutting oil or other liquid coolant (hereinafter referred to as a liquid coolant) is used conventionally for cooling a workpiece and a machining tool, thereby preventing a burning at a grinding or cutting point and removing cutting chips during the machining operation. Recently, in the interest of improving the working environment, there is designed a machining process with cold-gas-blow cooling in which a flow of cold gas (a stream of a gas having a low temperature) is used in place of the liquid coolant. This machining process with the cold-gas-blow cooling is advantageous over the conventional machining process in which the liquid coolant is used for cooling the workpiece and the machining tool, for example, in terms of freedom from splashes of the liquid coolant and also easier recycling of the cutting chips. However, since the gas used in the machining process with the cold-gas-blow cooling has a lower thermal conductivity and a smaller thermal capacity than those of the liquid, heat generated at the machining point is not sufficiently removed by the gas. Thus, the workpiece and the machining tool are likely to be affected by the generated heat, possibly causing problems such as deterioration of dimensional accuracy due to thermal expansion of the workpiece and deterioration of machining performance of the machining tool.
JP-A-56-9166 discloses a machining process including a machining step of machining the workpiece with a supply of a liquid coolant, and a cold-gas-blow machining-tool cooling step of cooling the machining tool with a supply of a cold gas blow. That is, when the workpiece has a predetermined dimension as a result of machining of the workpiece in the machining step, the machining step is followed by the cold-gas-blow machining-tool cooling step. In the cold-gas-blow machining-tool cooling step, the cold gas blow is supplied to the machining tool until the temperature of the machining tool (the temperature of the atmosphere within a cover covering the machining tool) is lowered to a predetermined temperature or less.
It is possible to apply this technique disclosed in the publication to a machining process having a machining step in which the liquid coolant is replaced by the cold gas blow such that the flow rate of the cold gas blow is controlled on the basis of the temperature of the machining tool during the machining operation. However, in this machining process, it is not possible to assure a sufficient cooling effect, thereby causing thermal expansion of the workpiece and deterioration of cutting performance of the machining tool, and possibly deteriorating machining accuracy.
The object of the present invention is to obtain a cold-gas-blow cooling machining process and a cold-gas-blow-cooling type machining apparatus which are capable of minimizing thermal influences on the workpiece and the machining tool. This object may be achieved by a machining apparatus or process according to any one of the following modes of the present invention, which are numbered and dependent from each other, where appropriate. It is to be understood that the following modes are provided to facilitate the understanding of the present invention, and that the technical features and the combinations of the technical features disclosed in the present specification are not limited to the following modes.
(1) A cold-gas-blow-cooling type machining apparatus including a relative movement device which moves a workpiece and a machining tool relative to each other, and a cold-gas-blow supply device which supplies a cold gas blow to a machining point at which the workpiece is machined by the machining tool, the machining apparatus being characterized by including:
a workpiece-temperature detecting device which detects a temperature of the workpiece; and
a machining-condition control device which controls at least one of the relative movement device and the cold-gas-blow supply device, on the basis of the temperature of the workpiece which is detected by the workpiece-temperature detecting device.
In the cold-gas-blow-cooling type machining apparatus described in the present mode, the temperature of the workpiece is detected by the workpiece-temperature detecting device. This workpiece-temperature detecting device may include a contact-type surface-temperature detecting device which is adapted to detect the temperature of the surface of the workpiece with its temperature sensor being brought into contact with the surface of the workpiece, or alternatively may include a non-contact-type surface-temperature detecting device which is adapted to detect the temperature on the basis of a radiant energy radiated from the workpiece. Since the workpiece radiates an electromagnetic wave having a wavelength distribution and an intensity which vary depending upon the temperature of the workpiece, the non-contact-type surface-temperature detecting device can detect the temperature of the workpiece without contact thereof with the workpiece, for example, by detecting a temperature rise of a subject body which is irradiated with the electromagnetic wave, or by detecting the intensity or wavelength of the electromagnetic wave. The non-contact-type surface-temperature detecting device may be a radiation thermometer or a thermography, for example.
The workpiece is one of sources which generate heat during the machining operation, and the generated heat directly affects the machining accuracy of the workpiece. In this view, it is appropriate to control the machining condition on the basis of the temperature of the workpiece. Where the cold-gas-blow supply device and the relative movement device are controlled on the basis of the temperature of the workpiece, the machining point can be effectively cooled, even where the cold gas blow has thermal capacity smaller than that of the liquid coolant, making it possible to obtain a suitable cooling effect. Thus, it is possible to minimize thermal expansion of the workpiece and deterioration of the machining performance of the machining tool, and accordingly minimize deterioration of the machining accuracy. That is, since the machining accuracy eventually affects the workpiece, the machining accuracy can be more effectively improved where the machining condition is controlled on the basis of the temperature of the workpiece, than where the machining condition is controlled on the basis of the temperature of the machining tool.
Further, in the cold-gas-blow-cooling type machining apparatus described in the present mode in which the liquid coolant is not used at all, there is no risk of deterioration of the working environment due to use of the liquid coolant.
It is noted that the cold-gas-blow-cooling type machining apparatus described in the present mode can be advantageously applied to a metallic-workpiece machining apparatus designed to machine a metallic workpiece which tends to be considerably thermally expanded in the machining operation. The cold-gas-blow-cooling type machining apparatus of the present mode in which the cutting condition is controlled on the basis of the temperature of the workpiece is suitable for machining a workpiece made of aluminum, copper, casting or other material having a comparatively large coefficient of linear expansion.
(2) A cold-gas-blow-cooling type machining apparatus according to mode (1), wherein the relative movement device includes a spindle which holds the workpiece and rotates the workpiece about an axis of the workpiece.
In the cold-gas-blow-cooling type machining apparatus described in the present mode, the workpiece is held and rotated by the spindle. The rotated workpiece and the machining tool are further moved relative to each other in at least one direction, whereby the workpiece is machined by the machining tool. The cold-gas-blow-cooling type machining apparatus of the present mode may be, for example, a lathe, or a grinding machine (e.g., a cylindrical grinding machine, an internal cylindrical grinding machine, and a centerless grinding machine).
(3) A cold-gas-blow-cooling type machining apparatus according to mode (2), wherein the temperature detecting device includes a detecting portion opposed to a point that lies on a circle on which the machining point lies and that is spaced apart from the machining point circumferentially of the workpiece, the circle having a center on the axis.
In the cold-gas-blow-cooling type machining apparatus described in the present mode, the temperature of the heat generation as a result of the machining operation can be accurately detected.
(4) A cold-gas-blow-cooling type machining apparatus according to any one of modes (1)-(3), wherein the machining-condition control device includes a cooling-condition control device which controls the cold-gas-blow supply device so as to control at least one of a temperature and a flow rate of the cold gas blow.
The control of the temperature and flow rate of the cold gas blow on the basis of the temperature of the workpiece makes it easy to perform a suitable cooling.
(5) A cold-gas-blow-cooling type machining apparatus according to mode (4), wherein the cooling-condition control device includes a workpiece-temperature controlling portion which controls at least one of the temperature and the flow rate of the cold gas blow such that the temperature of the workpiece is held within a predetermined range.
The temperature or flow rate of the cold gas blow is controlled such that the temperature of the workpiece is held between the upper and lower threshold values of the predetermined range. This control makes it possible to minimize a variation in the machining temperature during machining of the individual workpieces by the machining apparatus, thereby improving the machining accuracy. Further, it is possible to prevent the machining point from being excessively cooled, thereby minimizing an unnecessary consumption of energy by the cold-gas-blow supply device.
(6) A cold-gas-blow-cooling type machining apparatus according to any one of modes (1)-(5), wherein the machining-condition control device includes a relative-movement-condition control device which controls the relative movement device so as to control at least one of a velocity and an amount of relative movement of the workpiece and the machining tool.
Where the machining resistance is optimized by controlling the velocity of the relative movement of the workpiece and the machining tool on the basis of the temperature of the workpiece, it is possible to efficiently machine the workpiece while preventing an excessive rise of the surface temperature of the workpiece during the machining operation. Thus, the control of the velocity of the relative movement makes it possible to effectively cool the machining point even by the cold gas blow which has small thermal capacity. Further, where the amount of the relative movement is controlled on the basis of the temperature, it is possible to control a movement-stop position (final position) of the machining tool, by taking account of the thermal expansion of the workpiece. Thus, the control of the amount of the relative movement makes it possible to improve the machining accuracy of the workpiece.
The xe2x80x9crelative movementxe2x80x9d recited in the present mode may be a relative movement of the machining tool and the workpiece in a direction perpendicular to a machined surface of the workpiece (hereinafter simply referred to as the perpendicular direction) or a direction parallel to the machined surface of the workpiece (hereinafter simply referred to as the parallel direction). The velocity and amount of the relative movement in the perpendicular direction, or the velocity of the relative movement in the parallel direction may be controlled. Alternatively, both of them may be controlled.
Where the machining apparatus according to the present mode is applied to a cylindrical grinding machine so that a plunge grinding is performed by the cylindrical grinding machine, the velocity and amount of the relative movement of the grinding wheel and the workpiece W in the perpendicular direction (radial direction) are controlled. As described below in BEST MODE FOR CARRYING OUT THE INVENTION, where the relative movement device is controlled such that the grinding wheel and the workpiece are moved (fed) alternately toward and away from each other so that the workpiece W is intermittently ground by the grinding wheel, it takes a longer time to grind the workpiece by a predetermined amount, than where the workpiece W is continuously ground by the grinding wheel. Thus, where the workpiece W is intermittently ground by the grinding wheel, the average velocity of the relative movement in the perpendicular direction is considered to be reduced. Where a transverse grinding is performed by the cylindrical grinding machine, at least one of the relative movement in the perpendicular direction (radial direction or cutting depth direction) and the relative movement in the parallel direction (axial direction or feed direction) is controlled. The machining resistance can be increased or reduced also by increasing or reducing the velocity of the relative movement in the feed direction.
(7) A cold-gas-blow-cooling type machining apparatus according to mode (6), wherein the relative-movement-condition control device includes a machining-velocity reducing portion which reduces the velocity of the relative movement when the temperature of the workpiece rises to a predetermined temperature.
When the temperature of the workpiece rises to the predetermined temperature, the velocity of the relative movement in the perpendicular or parallel direction is reduced, thereby reducing the machining resistance and accordingly minimizing the heat generation amount. The machining velocity can be reduced also by intermittently machining the workpiece, and can be further reduced by prolonging a time of interruption of the machining in the intermittent machining.
(8) A cold-gas-blow-cooling type machining apparatus according to any one of modes (1)-(7), wherein the machining-condition control device includes a provisional target-dimension determining portion which calculates a provisional target-dimension of the workpiece as a target dimension of the workpiece upon completion of machining of the workpiece, on the basis of the temperature of the workpiece detected by the workpiece-temperature detecting device, and a provisional-target-dimension-basis relative-movement control portion which controls the relative movement device on the basis of the provisional target-dimension which is determined by the provisional-target-dimension determining portion, such that the machining is completed when the workpiece has the provisional target-dimension.
The provisional target-dimension is compensated on the basis of the temperature of the workpiece, thereby making it possible to perform a highly accurate machining even if the thermal expansion of the workpiece is increased due to the small thermal capacity of the cold gas blow. That is, the workpiece is machined while it is being thermally expanded, and the workpiece is then contracted when the temperature is lowered to the normal temperature. The contraction amount is larger where the temperature of the workpiece during the machining operation is comparatively high, than where the temperature during the machining operation is comparatively low. In this view, if the provisional target-dimension is compensated such that the provisional target-dimension is made larger where the temperature during the machining operation is comparatively high, than where the temperature is comparatively low, it is possible to minimize a variation in the dimension of the workpiece after the temperature has been lowered to the normal temperature, thereby improving the machining accuracy of the workpiece.
The provisional target-dimension of the workpiece is thus determined on the basis of the temperature of the workpiece. It is preferable to determine the provisional target-dimension by taking account of also the coefficient of linear expansion of the workpiece, a definitive target-dimension of the workpiece at a standard temperature, and other factors. For example, the provisional target-dimension d can be obtained according to the following equation:
d=Dxc3x97{1+xcex1(txe2x88x92T)}
wherein D, t, and xcex1 represent the definitive target-dimension of the workpiece at the standard temperature T, the detected temperature of the workpiece, and the coefficient of linear expansion of the workpiece, respectively. Further, for obtaining the provisional target-dimension, it is also possible to take account of a hardness, elastic coefficient or other physical properties of the workpiece, the temperature of the machining tool, the temperature of the body of the machining apparatus, and the external temperature, in addition to the coefficient of linear expansion of the workpiece.
(9) A cold-gas-blow-cooling type machining apparatus according to any one of modes (1)-(8), wherein the cold-gas-blow supply device includes a first cold-gas-blow supply device which supplies the cold gas blow to the machining point, and a second cold-gas-blow supply device which supplies the cold gas blow to a portion of the workpiece that is different from the machining point.
The workpiece, whose machining accuracy is directly affected by the heat generation, can be more sufficiently cooled even by the cold gas blow where the portion different from the machining point also is cooled, than where the cold gas blow is supplied to only the machining point. Further, since the flow rate and temperature of the cold gas blow supplied from the second cold-gas-blow supply device, as well as the flow rate and temperature of the cold gas blow supplied from the first cold-gas-blow supply device, are controlled, the temperature and dimension of the workpiece can be further accurately controlled. The first and second cold-gas-blow supply devices may include common devices and respective exclusive devices. That is, the two cold-gas-blow supply devices may commonly use a tank, a compressor and a cooling device, and use respective conduits and supply nozzles. Alternatively, each of the two cold-gas-blow supply devices may exclusively use a tank, a compressor, a cooling device, a conduit and a supply nozzle.
Where the workpiece is rotatably held by the spindle, it is preferable that the second cold-gas-blow supply device supply the cold gas blow on the downstream side of the machining point of the workpiece in the rotating direction. The supply of the cold gas blow on the downstream side of the machining point makes it possible to effectively cool the point which is particularly heated during the machining operation. If the portion to which the cold gas blow is supplied by the second cold-gas-blow supply device is located on the downstream side of the machining point and is adjacent to the machining point, this portion can be cooled immediately after the portion is heated.
Further, the cold-gas-blow supply device may further include a machining-tool cold-gas-blow supply device which cools the machining tool with the cold gas blow, thereby further improving the cooling effect.
The machining-condition control device does not necessarily have to control both of the first and second cold-gas-blow supply devices, but has only to control either one of them. Where one of them is controlled, it is preferable to control the second cold-gas-blow supply device. It is preferable to permit the first cold-gas-blow supply device to always carry out the sufficient cooling performance, since the first cold-gas-blow supply device serves to supply the cold gas blow to the machining point. This means a relatively small need for controlling the temperature and flow rate of the cold gas blow supplied from the first cold-gas-blow supply device. The temperature and flow rate of the cold gas blow supplied from the second cold-gas-blow supply device, on the other hand, can be advantageously controlled over wider ranges, whereby the workpiece can be suitably cooled, avoiding an unnecessary energy consumption while improving the cooling effect. If both of the first and second cold-gas-blow supply devices are controlled, it is possible to control the temperature of the workpiece with an improved response.
(10) A cold-gas-blow-cooling type machining apparatus according to mode (9), further comprising a covering member which covers at least the portion to which the cold gas blow is supplied by the second cold-gas-blow supply device such that the covering member and the portion are spaced apart from each other by a suitable distance, whereby the covering member guides the cold gas blow along a surface of the workpiece.
The cold gas blow is permitted to stream along the surface of the workpiece, owing to the provision of the covering member that covers the portion of the workpiece to which portion the cold gas blow is supplied, thereby increasing the cooling effect. The covering member has only to cover at least the portion to which the cold gas blow is supplied, and may cover the portion and its periphery as well, or alternatively cover a major part of the workpiece. It is noted that the covering member can be considered as a component constituting a part of the second cold-gas-blow supply device.
(11) A cold-gas-blow-cooling type machining apparatus according to mode (10), wherein the covering member is movable toward and away from the workpiece.
The covering member has only to be movable toward and away from the workpiece. The covering member may be removable from the machining apparatus, or may be linearly movable or rotatable. In any one of these cases, it is possible to suitably move the covering member, such that the covering member does not interfere with an operation to set the workpiece in the machining apparatus, or such that the cooling effect is further increased.
(12) A cold-gas-blow cooling machining process of machining a workpiece, which is attached to a spindle, by a machining tool with a relative movement of the workpiece and the machining tool, while supplying a cold gas blow to a machining point at which the workpiece is machined by the machining tool, the machining process being characterized by:
monitoring a temperature of the workpiece, and holding a variation in the temperature caused by machining of the workpiece by the machining tool, within a predetermined range.
According to the machining process described in the present mode, the variation in the temperature of the workpiece can be held within the predetermined range, thereby providing an improved machining accuracy and some other advantages.
(13) A cold-gas-blow cooling machining process of machining a workpiece, which is attached to a spindle, by a machining tool with a relative movement of the workpiece and the machining tool, while supplying a cold gas blow to a machining point at which the workpiece is machined by the machining tool, the machining process being characterized by:
controlling at least one of a temperature and a flow rate of the cold gas blow, on the basis of a temperature of the workpiece.
(14) A cold-gas-blow cooling machining process of machining a workpiece, which is attached to a spindle, by a machining tool with a relative movement of the workpiece and the machining tool, while supplying a cold gas blow to a machining point at which the workpiece is machined by the machining tool, the machining process being characterized by:
controlling at least one of an amount of the relative movement of the workpiece and the machining tool, and a velocity of the relative movement, on the basis of a temperature of the workpiece.
(15) A cold-gas-blow cooling machining process according to mode (14), further comprising a velocity reducing step of reducing a velocity of the relative movement when the temperature of the workpiece rises to a predetermined temperature.
The velocity reducing step includes an intermittently machining step, as described above. Where the cold-gas-blow cooling machining step according to the present invention is applied to a plunge grinding performed in a cylindrical grinding machine, for example, the movement of the grinding wheel and the workpiece W toward each other is suspended at a point of the time when the temperature of the workpiece rises to a machining suspending temperature. The grinding wheel and the workpiece W are then moved away from each other. At the time when the temperature is lowered to a machining resuming temperature, the grinding wheel and the workpiece W are moved toward each other again.
(16) A cold-gas-blow cooling machining process according to mode (14) or (15), further comprising a step of determining a provisional target-dimension of the workpiece as a target dimension of the workpiece upon completion of machining of the workpiece, on the basis of the temperature of the workpiece, a coefficient of linear expansion of the workpiece, and a definitive target-dimension of the workpiece as a target dimension of the workpiece at a standard temperature, and a step of controlling the amount of the relative movement of the workpiece and the machining tool, on the basis of the provisional target-dimension.
(17) A cold-gas-blow cooling machining process according to any one of modes (12)-(16), wherein the cold gas blow is supplied to the machining point and also a portion of the workpiece which is distant from the machining point.